1) Field of the Invention
The present invention relates to an ATM (Asynchronous Transfer Mode) communication system, and a congestion state detection method and an ATM communication device in the ATM communication system.
2) Description of the Related Art
ATM is a technique of transferring information, which is provided with high-speed switching by hardware processing and provides high quality of services (QOS) which is sufficient for realizing multimedia data communication. The ATM technology has been developed as practicable technology by the efforts of the organizations such as the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) and the ATM Forum.
In addition, various products and services in accordance with a number of standards for the ATM technology have been provided by manufacturers and carriers, and a large market of the ATM products and services has already been developed. In particular, interworking between high-speed, high-quality ATM communication networks for using the Internet. technology over such ATM communication networks are intensively studied. The study is also conducted by IETF (the Internet Engineering Task Force), in addition to the above organizations.
The ATM technology was first used as a backbone of a LAN (Local Area Network). At that time, a typical LAN used the Ethernet, and the mainly used transmission rate of the Ethernet was 10 Mbps or 100 Mbps. On the other hand, the mainly used rate of interface of ATM communication networks was 156 Mbps. Therefore, the ATM communication networks functioned well as a backbone of the above LAN. Recently, the 100 Mbps Ethernet is dominant, and further the Gigabit Ethernet having the transmission rate of 1 Gbps is supplanting the ATM.
However, faster interfaces for ATM, such as ATM interfaces having the transmission rates of 2.4 Gbps and 10 Gbps, have been standardized, while the speeding up of the Ethernet seems to be near the limit.
Under the above circumstances, the ATM technology was next used in a wide area service in which a plurality of private networks (e.g., LANs) are connected to each other. Although, conventionally, high-speed digital dedicated-line services are mainly used for connections between the private networks in a wide area service, only a small number of predetermined transmission rates are provided by such high-speed digital dedicated-line service, and gaps-between the values of the predetermined transmission rates are great. Therefore, it is necessary to bundle more than one dedicated line or use a dedicated line having excessive bandwidth for satisfying user""s requirement.
On the other hand, in the ATM dedicated-line services, virtual channels (VCs) can be set as permanent virtual connection in small unit amounts. For example, in the ATM Mega Link Service, which is currently provided by NTT Communications Corporation in Japan, users can select the transmission rate in 1 Mbps increments in the range of 1 to 135 Mbps. As another example, the Super Relay Service is a virtual channel (VC) service, which is also provided by NTT Communications Corporation in Japan. The Super Relay Service provides a number of options for the transmission rate, such as 16 Kbps, 32 Kbps, 48 Kbps, . . . 1 Mbps, 2 Mbps, . . . 10 Mbps, in the low transmission rate range, and a switched virtual connection (SVC) service.
In addition, due to the statistical multiplexing gain in the ATM technology, network service providers can reduce equipment investment and lower service tariff to reduce users"" cost. It is expected that the ATM services are further diversified in the future to provide further options corresponding to various needs of users.
In the ATM services, a plurality of service categories are provided to cope with various traffic characteristics. For example, the ATM Forum Traffic Management Specification Version 4.0 (af-tm-0056.0) provides the following four service categories:
(i) CBR (Constant Bit Rate)
In the CBR service, users"" cell transmission rates are completely guaranteed within a range defined by a Peak Cell Rate (PCR). The service category CBR achieves quality corresponding to the conventional dedicated-line service.
(ii) UBR (Unspecified Bit Rate)
The UBR service is a best-effort service, in which users"" cell transmission rates are not guaranteed even under the PCR. When congestion occurs in the network, cells may be discarded. In ATM-LANs, traffic is generally controlled in the manner of the UBR service.
(iii) VBR (Variable Bit Rate)
The VBR service guarantees a contracted Sustainable Cell Rate (SCR) as an average of cell transmission rates from a user when congestion does not occur in the network. For cell transmission rates exceeding the Sustainable Cell Rate (SCR) and not exceeding the PCR, the VBR service is a best-effort service like the UBR service. It is generally said that the VBR service is suitable for bursty traffic.
(iv) ABR (Available Bit Rate)
The ABR service guarantees users"" cell transmission rates under a Minimum Cell Rate (MCR). In addition, the ABR service includes notification of a state of resources in the network or a receiver-side (destination) endsystem to a transmitter-side (source), endsystem. Therefore, the transmitter-side endsystem can vary a cell transmission rate between the Minimum Cell Rate (MCR) and the Sustainable Cell Rate (SCR) in response to the notified state of resources.
Only three of the above service categories, CBR, UBR, and VBR, are provided in the ATM communication networks currently operating in the world. However, the UBR and VBR services do not include notification of congestion, although cells may be discarded under these services. That is, the currently operating networks do not have a function of notifying an endsystem of occurrence of congestion.
FIG. 24 shows endsystems which transmit cells from one to the other through an ATM communication network. In FIG. 24, the endsystems are ATM routers 100 and 200, and the ATM communication network 300 does not have the function of notifying an endsystem of occurrence of congestion. Therefore, endsystems such as ATM routers 100 and 200 in FIG. 24 cannot perform, in the ATM layer, control (e.g., reduction) of cell transmission rates corresponding to the occurrence of congestion (i.e., discard of a cell) in the ATM communication network such as the network 300 in FIG. 24, and the endsystems using the UBR or VBR service of the conventional ATM communication network usually send cells at the PCR on the premise that cells may be discarded.
As described above, when the UBR or VBR service of the conventional ATM communication network is used, cells may be discarded due to occurrence of congestion. Nevertheless, the current network does not have functions of detecting and notifying the occurrence of congestion. Actually, ATM-exchanges or the like which constitute the ATM communication network do not have the above functions. Thus, endsystems cannot be informed of the occurrence of congestion (and discard of a cell), and therefore cannot perform cell rate control for coping with or avoiding the occurrence of congestion.
If a function of retransmitting a discarded cell is provided in another layer above the ATM layer, it is possible to recover information contained in the discarded cell. However, the congestion per se cannot be avoided unless the cell rate control is performed in the ATM layer.
On the other hand, if the ATM communication network provides the aforementioned ABR service, the ATM communication network has the function of notifying an endsystem of occurrence of congestion. Therefore, endsystems can recognize the occurrence of congestion, and perform the cell rate control. However, in order to implement the ABR service in the conventional ATM communication network, all of the endsystems and the ATM communication network including all the ATM exchanges and other constituents of the ATM communication network need substantial modification. Therefore, considering design, manufacturing, and cost, it is not advantageous to modify the conventional ATM communication network for implementing the ABR service function. In addition, it lacks flexibility in construction of the network.
In addition, the ABR service must guarantee the bandwidth for the Minimum Cell Rate (MCR) completely. Therefore, the ABR service may preoccupy bandwidth for other services to impede effective utilization of resources (in particular, bandwidth). Namely, the implementation of the ABR service is disadvantageous.
An object of the present invention is to provide an ATM communication system containing an ATM communication network and a plurality of endsystems, wherein a congestion state of the ATM communication network can be detected easily by the endsystems without modification of or functional addition to the ATM communication network.
Another object of the present invention is to provide a congestion state detection method executed in the ATM communication system containing an ATM communication network and a plurality of endsystems, whereby a congestion state of the ATM communication network can be detected easily by the endsystems without modification of or functional addition to the ATM communication network.
A further object of the present invention is to provide an ATM communication device which can be connected to an ATM communication network for transmitting cells to and receiving cells from a second ATM communication device connected to the ATM communication network, where the ATM communication device can detect a congestion state of the ATM communication network or assist the second ATM communication device in detecting a congestion state of the ATM communication network.
According to the first aspect of the present invention, there is provided an ATM communication system having an ATM communication network and a plurality of ATM communication apparatuses connected to the ATM communication network, where data is transmitted from a first one of the plurality of ATM communication apparatuses to a second one of the plurality of ATM communication apparatuses through a logical connection set in the ATM communication network. The first one of the plurality of ATM communication apparatuses contains a transmission-data-amount counting unit which counts an amount of transmission data to the logical connection, and a notification processing unit which sends to the second one of the plurality of ATM communication apparatuses a notification containing the amount of transmission data counted by the transmission-data-amount counting unit. The second one of the plurality of ATM communication apparatuses contains a reception-data-amount counting unit which counts an amount of reception data which have been received from the logical connection, and a congestion-state detecting unit which can detect a congestion state of the ATM communication network by comparing the amount of transmission data contained in the notification sent from the first one of the plurality of ATM communication apparatuses, with the amount of reception data counted by the reception-data-amount counting unit.
According to the second aspect of the present invention, there is provided an ATM communication system having an ATM communication network and a plurality of ATM communication apparatuses connected to the ATM communication network, where data is transmitted from a first one of the plurality of ATM communication apparatuses to a second one of the plurality of ATM communication apparatuses through a logical connection set in the ATM communication network. The first one of the plurality of ATM communication apparatuses contains a first predetermined-amount storing unit which stores information indicating a predetermined amount, a transmission-data-amount counting unit which counts an amount of transmission data which have been transmitted to the logical connection, and a notification processing unit which sends to the second one of the plurality of ATM communication apparatuses a notification that transmission data corresponding to the predetermined amount have been transmitted, when the amount of transmission data counted by the transmission-data-amount counting unit after a previous notification reaches the predetermined amount. The second one of the plurality of ATM communication apparatuses contains a second predetermined-amount storing unit which stores the information indicating the predetermined amount, a reception-data-amount counting unit which counts an amount of reception data which have been received after reception of the previous notification from the logical connection, and a congestion-state detecting unit which detects a congestion state of the ATM communication network, based on a result of comparison between the predetermined amount and the amount of reception data counted by the reception-data-amount counting unit until the notification is received after reception of the previous notification.
According to the third aspect of the present invention, there is provided a congestion state detection method for detecting a congestion state in an ATM communication system having an ATM communication network and a plurality of ATM communication apparatuses connected to the ATM communication network, where data is transmitted from a first one of the plurality of ATM communication apparatuses to a second one of the plurality of ATM communication apparatuses through a logical connection set in the ATM communication network. The method contains the steps of (a) sending from the first one of the plurality of ATM communication apparatuses to the second one of the plurality of ATM communication apparatuses an amount of transmission data to the logical connection; and (b) detecting a congestion state of the ATM communication network by comparing the amount of transmission data sent from the first one of the plurality of ATM communication apparatuses, with an amount of reception data which have been actually received by the second one of the plurality of ATM communication apparatuses.
According to the fourth aspect of the present invention, there is provided a congestion state detection method for detecting a congestion state in an ATM communication system having an ATM communication network and a plurality of ATM communication apparatuses connected to the ATM communication network, where data is transmitted from a first one of the plurality of ATM communication apparatuses to a second one of the plurality of ATM communication apparatuses through a logical connection set in the ATM communication network. The method contains the steps of (a) storing information indicating a predetermined amount in the first and second ones of the plurality of ATM communication apparatuses; (b) sending from the first one of the plurality of ATM communication apparatuses to the second one of the plurality of ATM communication apparatuses a notification that transmission data corresponding to the predetermined amount have been transmitted, when transmission data which have been transmitted after a previous notification from the first one of the plurality of ATM communication apparatuses to the logical connection reaches the predetermined amount; and (c) detecting a congestion, state of the ATM communication network based on a result of comparison between the predetermined amount and an amount of reception data which have been received by the second one of the plurality of ATM communication apparatuses from the logical connection until the notification is received after reception of the previous notification.
According to the fifth aspect of the present invention, there is provided a transmitter-side ATM communication apparatus connected to an ATM communication network, where data is transmitted from the transmitter-side ATM communication apparatus to a receiver-side ATM communication apparatus through a logical connection set in the ATM communication network. The transmitter-side ATM communication apparatus contains a transmission-data-amount counting unit which counts an amount of transmission data to the logical connection; and a notification processing unit which sends to the receiver-side ATM communication apparatus a notification containing the amount of transmission data counted by the transmission-data-amount counting unit, so that the receiver-side ATM communication apparatus can detect a congestion state of the ATM communication network by comparing the amount of transmission data with an amount of reception data which have been actually received by the receiver-side ATM communication apparatus.
According to the sixth aspect of the present invention, there is provided a transmitter-side ATM communication apparatus connected to an ATM communication network, where data is transmitted from the transmitter-side ATM communication apparatus to a receiver-side ATM communication apparatus through a logical connection set in the ATM communication network. The transmitter-side ATM communication apparatus contains a predetermined-amount storing unit which stores information indicating a predetermined amount; a transmission-data-amount counting unit which counts an amount of transmission data which have been transmitted to the logical connection; and a notification processing unit which sends to the receiver-side ATM communication apparatus a notification that transmission data corresponding to the predetermined amount have been transmitted, when transmission data corresponding to the predetermined amount have been transmitted to the logical connection after a previous notification, so that the receiver-side ATM communication apparatus can determine whether or not the ATM communication network is in a congestion state by comparing the predetermined amount with an amount of reception data which have been received from the logical connection until the notification sent by notification processing unit is received by the receiver-side ATM communication apparatus after the previous notification.
According to the seventh aspect of the present invention, there is provided a receiver-side ATM communication apparatus connected to an ATM communication network, where data is transmitted from a transmitter-side ATM communication apparatus to the receiver-side ATM communication apparatus through a logical connection set in the ATM communication network. The receiver-side ATM communication apparatus contains a reception-data-amount counting unit which counts an amount of reception data which have been received from the logical connection; and a congestion-state detecting unit which can detect a congestion state of the ATM communication network by comparing an amount of transmission data which have been transmitted from the transmitter-side ATM communication apparatus to the logical connection, with the amount of reception data counted by the reception-data-amount counting unit when the amount of transmission data is informed by the transmitter-side endsystem.
According to the eighth aspect of the present invention, there is provided a receiver-side ATM communication apparatus connected to an ATM communication network, where data is transmitted from a transmitter-side ATM communication apparatus to the receiver-side ATM communication apparatus through a logical connection set in the ATM communication network. The receiver-side ATM communication apparatus contains a predetermined-amount storing unit which stores information indicating a predetermined amount, which is also stored in the transmitter-side ATM communication apparatus; a reception-data-amount counting unit which counts an amount of reception data which have been received from the logical connection; and a congestion-state detecting unit which can detect a congestion state of the ATM communication network, based on a result of comparison between the predetermined amount and the amount of reception data which have been received from the logical connection until a notification is received, from the transmitter-side endsystem after a previous notification, where the notification indicates that transmission data corresponding to the predetermined amount have been transmitted from the transmitter-side ATM communication apparatus to the logical, connection after a previous notification.
As described above, in the ATM communication system according to the first aspect of the present invention and by the congestion state detection method according to the third aspect of the present invention, the transmitter-side ATM communication apparatus sends to the receiver-side ATM communication apparatus an amount of transmission data which have been transmitted from the transmitter-side ATM communication apparatus to the logical connection. Receiving the amount of transmission data, the receiver-side ATM communication apparatus compares the amount of transmission data with an amount of reception data which have been actually received by the receiver-side ATM communication apparatus. Therefore, the receiver-side ATM communication apparatus can determine whether or not the ATM communication network is in a congestion state. That is, even when the ATM communication network does not have the function of notifying an endsystem of occurrence of congestion, the congestion state of the ATM communication network can be detected by the functions which are provided in the ATM communication apparatuses only, without modifying or adding a function to the ATM communication network.
The fifth aspect of the present invention provides the transmitter-side ATM communication apparatus in the above ATM communication system according to the first aspect of the present invention, and the seventh aspect of the present invention provides the receiver-side ATM communication apparatus in the above ATM communication system according to the first aspect of the present invention.
Also, as described above, in the ATM communication system according to the second aspect of the present invention and by the congestion state detection method according to the fourth aspect of the present invention, the information indicating a predetermined amount is stored in advance in both the transmitter-side and receiver-side ATM communication apparatuses. Every time transmission data corresponding to the predetermined amount have been transmitted to the logical connection, the transmitter-side ATM communication apparatus notifies the receiver-side ATM communication apparatus that transmission data corresponding to the predetermined amount have been transmitted from the transmitter-side ATM communication apparatus. Receiving the notification, the receiver-side ATM communication apparatus compares the predetermined amount with an amount of reception data which have been actually received by the receiver-side ATM communication apparatus from the logical connection until the notification is received after the previous notification. Thus, the receiver-side ATM communication apparatus can determine whether or not the ATM communication network is in a congestion state, based on the comparison result. In this case, only the above notification and transmission data are required to be sent from the transmitter-side ATM communication apparatus to the receiver-side ATM communication apparatus. Therefore, congestion can be detected with a smaller amount of overhead.
The sixth aspect of the present invention provides the transmitter-side ATM communication apparatus in the above ATM communication system according to the second aspect of the present invention, and the eighth aspect of the present invention provides the receiver-side ATM communication apparatus in the above ATM communication system according to the second aspect of the present invention.